Chemistry

Dr. Sayan Bhattacharyya
IISER Kolkata

Abstract: The conversion of solar energy directly into fuels is a promising solution to the societal pursuit of next-generation clean and renewable energy addressing energy conversion, storage and transport. Photoelectrochemical cells offer a promising method for hydrogen gas production via water splitting but the solar-to-hydrogen efficiencies are highly limited by the band gap and corrosion of semiconductor electrodes. The other option is to connect solar cells in series to generate the applied voltage required for water electrolysis. The potential utility of the photovoltaics driven water electrolysis is dependent on optimization of the open circuit voltage in solar cells and cost-effective electrocatalysts that can operate at reduced overpotential generating high current densities. In spite of the rapidly increasing attention towards perovskite solar cells, exploiting semiconductor quantum dots (QDs) as solar harvesters constitutes a promising approach towards low-cost third-generation photovoltaic devices. Moreover, QD solar cells (QDSCs) are expected to cross the Shockley-Queisser power conversion limit of ~32%. A major contributor to the sub-par performance of QDSCs is the interfacial charge recombination at the TiO2/QD-electrolyte interface. We have developed few strategies to boost the power conversion efficiency (PCE) of QDSCs. The first strategy is the intentional heteroatom doping in colloidal QDs to increase the lifetime of excited charge carriers,1 the second being a novel dual sensitization strategy of core/shell QDs through optimization of QD pH and thicknesses of QD layers,2 and the third is tuning the electrocatalytic activity of counter electrodes. On the other hand, we have employed microwave synthesized carbon dots as abundant non-metal catalysts for water splitting. The carbon dots operate at a decently low overpotential and can generate high current densities as a welcome alternative to the expensive IrO2 and RuO2. The results are also superior to many of the best performing metal containing catalysts.3-5 The strategic microwave synthesis results in trapping of anti-oxidant within the carbon dots, which can easily extract the intermediate radicals and facilitate the forward reaction of H2O splitting. This lecture will discuss these experimentally verified propositions that have overreaching consequences.